tile shower stall leaking - seems to be grout help!

We have a tile shower stall with a fairly new pan (2-3 years, maybe). It leaks after some showers. We have access to the plumbing behind, and we've opened up areas below and at floor level behind and in hallway beside (where we see moisture after showers if it happens - doesn't take long, right after shower). (Also house is 1914, but shower is about 25 years old). Tile appears to be solid. Tile man who did some caulking for us knocked on it, etc. Said it was good - concreteboard backing looks OK where we can can see it (so not the obvious problems I've seen in other posts).

I tested as follows:
- ran hose directly from shower pipe to drain - 1/2 hour or so - nothing
- plugged drain and flooded pan 20 min-1/2 hour - nothing.
- hung plastic over right 2/3 (including plumbing fixtures below showerhead) - took a week + of showers by 2 of us - nothing
- shifted the plastic to cover only the right side, uncover plumbing fixtures - nothing after first shower, but some after my wife's shower. drain backing up both times to 1-2 inches depth (about what I flooded the pan).

Handyman says it may be failed grout after 25 years. Any other possibilities? What to do?

Redoing a shower pan and leaving the rest can cause problems. Its always best to tear the whole thing down and start over. It could be anything though... Grout failure, bad seal around your faucet trim ring, preslope issues etc...
When the pan was redone did you replace the whole pan or just the tile? The weep holes could be clogged forcing water to saturate the mortar bed and out a crack somewhere.

IF the pan was installed properly, it makes no difference whether the "weep holes" are clogged or not, the shower should still not leak until the water overflows the door's sill. Your "diagnosis" appears to pinpoint the leak around the plumbing fixture's trim ring. Splash water DIRECTLY onto the wall above the faucet and see what happens. This will accelerate a process that happens gradually during a shower. IT probably "leaks" during your shower, but does not appear until later when someone else is taking their shower.

Your "diagnosis" appears to pinpoint the leak around the plumbing fixture's trim ring. Splash water DIRECTLY onto the wall above the faucet and see what happens. This will accelerate a process that happens gradually during a shower. IT probably "leaks" during your shower, but does not appear until later when someone else is taking their shower.

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+1 on leaking around the trim.

It could also be that the water deflects off of your wife's mammalian protuberances onto the trim ring. Or maybe there is a hand shower and she uses it differently.